Deadlock is a state when a set of blocked processes each holding a resource are waiting to acquire a resource held by another process in the set Deadlock can arise if the following four conditions hold simultaneously Mutual exclusion only one process at a time can use a resource Hold and wait a process holding at least one resource is waiting to acquire additional resources held by other processes No pre emption a resource can be released only voluntarily by the process holding it, after that process has completed its task Circular wait there exists a set P1, P2, , Pn of waiting processes such that P1 is waiting for a resource that is held by P2, P2 is waiting for a resource that is held by P3, , Pn1 is waiting for a resource that is held by Pn, and Pn is waiting for a resource that is held by P1 There are 4 choices for handling deadlocks Choice 1 Ensure that the system will never enter a deadlock state Deadlock Prevention ensure that the system will never enter a deadlock state Deadlock Avoidance maintain the safe state by having the information about the maximum number of resources of each type it may need Choice 2 Allow the system to enter a deadlock state and then recover Deadlock Detection Deadlock Recovery Process Termination Abort all deadlocked processes, or abort one deadlocked process at a time until every deadlock cycle is eliminated May depend upon the priority of the process or process age and remaining time or resources the process has used or resources the process needs to complete or number of processes will need to terminated or the process are interactive or batch Resource Pre emption by selecting a victim or Rollback by return to some safe state, i e restart the current process Choice 3 Ignore and dont care Resources may be a single instance or multiple instances Resource allocation and wait for graph occurs for single instances generally and bankers algorithm works for multiple instances Q1 Given five memory partitions of 100Kb, 500Kb, 200Kb, 300Kb, 600Kb (in order), how would the first fit, best fit, and worst fit algorithms place processes of 212 Kb, 417 Kb, 112 Kb, and 426 Kb (in order) Which algorithm makes the most efficient use of memory Q2 Consider the following segment table Process Base register Limit Register 0 219 600 1 2300 14 2 90 100 3 1327 580 4 1952 96 Are the following logical addresses possible for each process If yes, what will be the corresponding physical addresses for each process with its logical address written after comma a 0,430 b 1,10 c 2,500 d 3,400 e 4,112 Q3 Suppose that we have free segments with sizes 6, 17, 25, 14, and 19 Place a program with size 13kB in the free segment using first fit, best fit and worst fit

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Deadlock is a state when a set of blocked processes each holding a resource are waiting to acquire a resource held by another process in

Deadlock is a state when a set of blocked processes each holding a resource are waiting to acquire a resource held by another process in the set.

Deadlock can arise if the following four conditions hold simultaneously:

Mutual exclusion: only one process at a time can use a resource.

Hold and wait: a process holding at least one resource is waiting to acquire additional resources held by other processes.

No pre-emption: a resource can be released only voluntarily by the process holding it, after that process has completed its task.

Circular wait: there exists a set {P1, P2, ..., Pn} of waiting processes such that P1 is waiting for a resource that is held by P2, P2 is waiting for a resource that is held by P3, ..., Pn1 is waiting for a resource that is held by Pn, and Pn is waiting for a resource that is held by P1.

There are 4 choices for handling deadlocks:

Choice #1: Ensure that the system will never enter a deadlock state

Deadlock Prevention - ensure that the system will never enter a deadlock state
Deadlock Avoidance maintain the safe state by having the information about the maximum number of resources of each type it may need

Choice #2: Allow the system to enter a deadlock state and then recover

Deadlock Detection
Deadlock Recovery
1. Process Termination -Abort all deadlocked processes, or abort one deadlocked process at a time until every deadlock cycle is eliminated. May depend upon the priority of the process or process age and remaining time or resources the process has used or resources the process needs to complete or number of processes will need to terminated or the process are interactive or batch?
2. Resource Pre-emption by selecting a victim or Rollback by return to some safe state, i.e. restart the current process

Choice #3: Ignore and dont care

Resources may be a single instance or multiple instances. Resource allocation and wait for graph occurs for single instances generally and bankers algorithm works for multiple instances.

Q1. Given five memory partitions of 100Kb, 500Kb, 200Kb, 300Kb, 600Kb (in order), how would the first-fit, best-fit, and worst-fit algorithms place processes of 212 Kb, 417 Kb, 112 Kb, and 426 Kb (in order)? Which algorithm makes the most efficient use of memory?

Q2. Consider the following segment table:

Process Base register Limit Register

0 219 600

1 2300 14

2 90 100

3 1327 580

4 1952 96

Are the following logical addresses possible for each process? If yes, what will be the corresponding physical addresses for each process with its logical address written after comma?

a. 0,430

b. 1,10

c. 2,500

d. 3,400

e. 4,112

Q3. Suppose that we have free segments with sizes: 6, 17, 25, 14, and 19. Place a program with size 13kB in the free segment using first-fit, best-fit and worst fit?